BRZ Rally Car

¯\_(ツ)_/¯ said:

In reply to 95maxrider :

14" spring, 7" travel shock.  More of the space in the spring is open than taken up by coils, so I think it'll be fine unless I run a crazy amount of preload, but that concern is exactly why I run the longest spring that I can fit.

I may have missed it, but how did you decide what lengths you needed/wanted for the springs and shocks. 

In reply to Somebeach (Forum Supporter) :

Most of that happens on page 5, but if you have a question not answered there feel free to ask!

Lengths for that stuff were all basically a combination of "how much travel can I fit?" and "what can I actually buy?"

Staying tuned to hear how the Rallycross goes.

In other news, I just read that LSPR was cancelled for this year :-(

DC RallyX 3 and 4, Summit Point

Did the standard drill- car packed with tires/tools/cooler/tent, up at 4am, drive to Summit Point.  Change wheels, tape numbers on, say hi to rally friends:

So, as a bit of a refresher- last time I was here the car was on stock suspension with the swaybars removed, same tires, and had the ABS fuse pulled.  It's now slightly heavier, has about 40% more suspension travel, adjustable brake bias, and a whole lot more things that are my fault if they're wrong.  There were other frisbees in attendance, both of which had the TRD rally suspension and some sort of lift spacer installed (not pictured, the white turbocharged one, only in attendance on day 2):

Day 1 was on the barn course, which is nice and open and usually very grippy, and while my rallycross driving isn't quite up to the incredibly high standards required to do well in DC region's ultra competitive mod rwd class, the car is AWESOME.  A couple spins of the brake bias knob during the first runs got things balanced and I didn't have to touch it for the rest of the weekend, the brakes were perfect- I had to calibrate myself to being able to brake super late, and trail braking can tighten the line really nicely when needed.  The suspension felt great, was never hurting for travel, and the damping feels dead on according to the butt dyno.  Like I said, I'm far from perfect, but for both the morning and afternoon sessions I had the fastest single run in MR, even if I couldn't do it consistently and cleanly enough to be in the running for a win.

This thing really is amazing on dirt in the current configuration- you can adjust your line all the way through the corner with small throttle/steering/brake inputs without dumping much speed, and it puts down power well on the way out of the corner provided the surface is smooth.

Hung out that night, set up the tent, and turned in after a good few hours of rally BSing among new and old friends.  Then woke up bright and early the next morning because the karting championship guys over on the main track like to get their engines warmed up first thing:

Day 2 was the short course, which is tighter and rougher, and has more loose dirt and rocks to really spice things up.  I was super pleased with how the car handled the bumpy stuff, I could brake or turn just fine through the choppy parts, but putting down power was interesting- if one rear wheel got off into the dust it would spin until it dug down, and the other wheel didn't seem to do much.  Maybe it's my imagination, maybe it's the Torsen.  I also had one pretty memorable screwup which gave me a chance to test the skidplates, they seem to work well.

Yet again, cones and inconsistency bumped me down the order, but on my last run of the day before we cut things short due to lightning I put down the fastest single run in MR.  I'm not bragging about my driving but I'm totally bragging about the suspension.  

Changed wheels, pulled tape off, packed car, went home.  The only thing wrong with the car as far as I can tell is that the brake pedal feels a little funny at the very beginning of its' travel, I think some dust got into the pivot bushing.  Everything else is great.  This is going well.

You prob need a plated lsd in the rear if you will be lifting wheels. Since torsen puts it to the wheel in the air instead of both.

In reply to MrChaos :

I anticipated it having trouble when a wheel leaves the ground.  It's a little surprising to me that it seems to have some trouble when there's just a big disparity in grip, even with both wheels loaded, like when one side is in soft dirt and the other is on hard clay.  Still way better than an open diff, but the behavior is a little weird and takes some getting used to.

If I can figure out an inexpensive way to put together a proper LSD rear end I'll try it- if the only solutions are $1k+ aftermarket stuff I think I'll just live with the Torsen.

Is300 diff is the same as the brz diff. So you can find an open 3.9 diff from one and weld it for id say $250-300.

Yours should be a 4.1 so a 3.9 won't be too far off. I know later cars are 4.3.

I get inside wheel spin just turning on to certain roads with a little bit of sand or small pebbles, I can imagine that torsen is going to be tough to get traction with in your application. There's a couple mechanical LSD options available though, so it is at least something you can buy your way out of.

Forum-ing around, there seems to be some people swapping the same MkIII Supra diff you had in the XR in to the IS300, which theoretically would swap to the BRZ. Not sure what fab work that would require. Speaking with Santiago, he's got 5.29 gears (115mph theoretical max speed) but has stuck with the Torsen so far.

In reply to TXratti :

I know, real shame I sold all the diffs with it!  Santiago does go quick with the Torsen, and realistically it probably costs very little stage time since there are relatively few slow corners where it might be a problem.  We'll see, it seems like it's worth at least getting the IS300 diff I picked up apart for a look.

¯\_(ツ)_/¯ said:

In reply to TXratti :

I know, real shame I sold all the diffs with it!  Santiago does go quick with the Torsen, and realistically it probably costs very little stage time since there are relatively few slow corners where it might be a problem.  We'll see, it seems like it's worth at least getting the IS300 diff I picked up apart for a look.

Is300 people have swapped complete diffs into their cars from BRZ/FRS' all they had to do was put spacers on the mounts for proper driveline angles.

Im also still considering a brz/frs for a rallyx car

¯\_(ツ)_/¯ said:

In reply to TXratti :

I know, real shame I sold all the diffs with it!  Santiago does go quick with the Torsen, and realistically it probably costs very little stage time since there are relatively few slow corners where it might be a problem.  We'll see, it seems like it's worth at least getting the IS300 diff I picked up apart for a look.

I ... may or may not have 2 MkIII diffs sitting in my garage.. a 4.3 and a 3.9 LSD 

In reply to TXratti :

If one of them has a broken housing or a damaged flange or something I'd buy the LSD internals from it.

In reply to ¯\_(ツ)_/¯ :

Currently 2 full and complete diffs (including stub shafts with flanges). Meant to be shipped to the west coast but two diffs in a box is almost 200 lb and that leaves very few ways to ship affordably.

Checked everything over, and it seems fine.  This is odd for me, I don't really know what to do when nothing is broken.

In reply to ¯\_(ツ)_/¯ :

Drop the engine, pull the suspension and stare at it for a while?

Some awesome photos from Alan Olson:

Decided to take a look at the aluminum brick that has the ABS stuff in it:

Took it apart, this is the computer side:

And the valve body thing:

The first thing I did was just plug the computer back in and start the car- unfortunately this makes it go from a single benign ABS code to 5, some of which are more alarming and may put the car in limp mode given the wrong set of conditions, so I don't think I can lose the entire block.

Instead, I tried taking the heaviest part off:

Removing the motor saves around 2lbs.  Not as much as I'd hoped but everything seems happy again and is back to the single "open circuit" code which doesn't trigger a check engine light and has run perfectly for 4 days of rallycross:

Back to exploring the junkyard Lexus diff:

It came apart easily although the drain plug allen head was pre-stripped by someone:

8" ring gear, 10 bolts, 30 spline axles- this sure looks like stuff from the Supra/4runner/Pickup parts bin should fit.  I'll know more when the mk3 Supra diff I'm buying from TXratti arrives.

I'm at a little bit of a crossroads on underbody protection- I need to armor the fuel lines and the bottom of the tank somehow.  There are a number of options here:

Steel- Heavy but cheap.  Slightly worrysome that it makes sparks when rocks hit it considering it's protecting fuel stuff.

Aluminum- Harder to fab, more expensive than steel.  The "standard" choice for this task.

HDPE plastic- Cheap, easy, but I'm not convinced it's tough enough for the job.

My dumb composite idea- So, there's already an ABS plastic channel over the fuel lines.  I can buy similar plastic panels that bolt on to cover the underside of the fuel tank for like $30.  Then I could get a few yards of carbon-kevlar fabric, scuff up the surface of the plastic panels, mix up some epoxy, and lay up a few layers straight onto the factory plastic stuff.  This would theoretically be light, tough, retain as much ground clearance as possible, and cost about the same as doing aluminum everywhere.  Hmm.

I've done quite a bit of composite work, and it indeed can be crazy tough stuff.  I took an aircraft part with 8-plies of carbon fiber and hit it as hard as I could with a hammer, and saw no indications of damage or delamination.

On thinner sections - like 4 ply - kevlar is the magic ingredient for impact resistance.  Unbelievably tough stuff.  If you can vacuum-bag the part, that's even better.

Only x-factor is that it may not want to stick to your abs part.  You could test this ahead of time though.  Just scuff a spot on the abs, wipe with acetone to degrease, and lay down some fabric/epoxy and see if it cures tight.

Or just use the abs parts as a crude mold.  Lay up your part, trim, and throw away the original.  The geometry should just fine for your needs.

I was going bro suggest the mold option until Scott mentioned it. Who cares if it looks rough, you know it'll fit, including fastener locations. You could build up little nub ridges around the fasteners to protect them, too.

I'm thinking he should Kevlar the whole undercarriage just to be safe. 

I think I would attempt my first layer in fiberglass, just because it's easier to get it to conform to the plastic shape and will then be easier to get the kevlar to stick to.  I'm still on the fence about whether that makes any sense vs. just doing aluminum, though.